Pressure-trapping chamber for fuel pumps



E. L.. PEARsoN PRESSURE TRAPPING CHAMBER FOR FUEL PUMPS Filed NOV. 16, 1928 w w s-;

i fm@ w W v by@ for .Pe @Isola ffzess A Patented Oct. 7, 1930 UNITEDv STATE-sA PATENT OFFICE ENOCH L. PEABSON, OF CHICAGO, ILLINOIS, ASSIGNOR TO STEWART-WARNER CORPORA- TION, 0F CHICAGO, ILLINOIS, A CORPORATION OF 'VIRGINIA p 4massenan-'rmurme CHAMBER rois rUELrUMPs Application ld November 16,1928. Serial No. A319,958.

AThe purpose of this invention is to provide an improved construction in a pump for feeding fuel to an internal combustion engine, particularly with respect to what is commonly called the air dome or trap chamber for accumulating pressure during the feeding stroke of the pump for maintaining continuous flow in the intervals between feeding strokes. The invention consists in the elements and features of construction shown and described as indicated in the claims.

The drawing is a vertical section axial with respect' to the `pumping chamber, discharge pipe and pressure trap. A

The invention is illustrated in connection with a well-known type of fuel pump in which the pumpin member is a diaphragm, A, the fuel intake rom thefuel source being by way of a filter and fuel vreserve chamber, B, past from which the fuel is discharged by the discharge pipe, E, past the check valve, F, beyond which check valve there is connected to the discharge pipe av pressure-trapping device above referred to as the air dome which embodies the present invention.

This pressure-trapping device as illustrated consists of a tubular member, 20, closed at its upper end and interiorly threaded at its lower end for connecting it with the upper end of the pump vcasing by means of a coupling, l22, which is screwed into an upwardly projecting nipple, 23, which terminates the 'pump casing ,directly abovev the seat, 24, of the dlscharge valve, F., said coupling having a cen trally projectingv pin, 26, for checking the opening movement of the check valve, and a light spring, 2 7, being providedv coiled about the pin reacting between the coupling and the discharge valve for insuring the seating of the latter. The coupling, 22, has a slender bore, 28, constituting the fluid communication withithe cavity'of theair dome member, 20, said bore being positioned obliquely for avoiding the pin, 26.

It will be understood that the coupling j 'makes air-tight junction both with the pump casing and with the air dome member, 20. Said air dome member, 20, bein cylindrical, as stated, has loosely fitted sli ingly 1n 1t a plunger, 30,and a coil spring, 31, is provided lnterposed below said plunger member reactingbetweenthe same and the upper end of the coupling, 22, the plunger member vand spring being dimensioned relatively tothe cylindrical air dome member, 20, so that a substantial air s ace remains in the air dome above the position ofthepiston in the original assembly 1n column in the discharge pipe.

' The operation of this construction may bek understood from the above description to the intent that in the feeding strokes of the pump the fuel filling the discharge pipe to the carbureter of the engine served, the liquid column in the discharge pipe operates througlha restricted bore, 28, to compress the air in t e dome bothbelow and above the plunger,- the liquid accumulating to some extent below the check valve, C, into the pumping chamber, D, plunger but not reaching the plunger because of the 'air trapped there-below inthe space occupied bythe spring and subject to compression, as stated, the plunger remaining substantially unchanged in the position at which it is upheld by the spring, 31, and that position being at a `higher point than the liquid can reach bycompressing the air to the maximumdegree which can result from the action of the pump in feeding the liquid to the carbureter, and thereby producing a liquid column of given maximum height and operating with a given4 pressure on the trapped air.`

The fit of the plunger inl` the cylindrical cavity of the dome, While not a piston t, is close enough so that liquid which might reach the lower surface of the plunger by any means, will tend to be drawn bycapillary attraction into the crevice between the plunger and the `cylinder wall, and operate asa liquid seal, converting the plun' er into a piston, to the extent-that the air will not pass it'from below under the pressure 'of the liquid column or the feeding stroke of the pump diaphragm, but, on the contrary, any increase of pressure will operate to force the plunger upward in the chamber, transmitting the pressure to the air above' it, so that the latter will be compressed to the same degree as the air below thel plunger.

the absence of any pressure rfrom the liquid pose is to damp the pulsations due to the resilient reaction of the pumping diaphragm and the compression resulting therefrom of the air confined and under pressure in the air dome.' ThisV is effected by the inertia of the plunger and the limited resistance to its move- Y ment which is caused by its fit in the cylinder 'of the dome,'notwithstanding that fit is rela.- tively loose as compared with the piston fit and causes only limited frictional resistance even when the plunger becomes liquid-sealed,

as above described.

nd upon consideration it may be understood that the relative freedom of movement of the plunger thus loosely fitted, even when liquid-sealed as compared with the condition as to the freedom of movement of the two pistons, brings into operation for the damplng of the turbulence of the confined air the inertia'of the plunger, as it would not be brought in usefull if the plunger were more or less positively eld by piston fit. And it may be further understood that if the p1unger were piston-fitted, so that it would not move under the. momentary changes of pressure which tend to cause turbulency, the body of air below such plunger piston would act just as if the plunger were the fixed top of an air trapping cavity; and the undesirable turbu- .lency would be experienced in said body of air without any relief by the damping effect of the freely moving plunger.

l: In combination with a pump for supplying fuel to an internal combustion engine an air trapping chamber connected with the pump discharge pipe beyond the pump dis charge valve, said chamber having a cylindrical portion and a plunger of substantial welght loosely fitted therein, enclosing a substantial air space between it and the closed end of the chamber, and a spring reacting on the plunger for spacing it away from the entrance to the chamber.` i V I 2. In combination with a pum for supplying fuel to an internal combustion engine, an air trapping chamber connected with the pump discharge pipe beyond the pump discharge valve, said chamber having a c lindrical portion and a plunger loosely tted therein, enclosing a substantial air space be" tween it and the closed end of the chamber, a spring irlfiterposed at the opposite side of the piston from said closed end and reacting for yieldingly forcing the plunger a limited distance into the cyllnder, the plunger being dimensioned for fitting the cylinder closely enough to be liquid-sealed by liquid which may be drawn into the crevice between the plunger and the cylinder wall by capillary attraction; whereby upon fluid pressure tending to compress the air in the dome at the entrance side of the plunger, the plunger operates for transmitting said pressure to the air between said plunger and the closed end of the dome.

3. In combination with a pump for supplying fuel to an internal combustion engine, a vertically extending air trapping chamber connected at its lower end with the pump discharge pipe beyond the pump discharge valve,

enclosed at its upperend, said chamber having a cylindrical portion intermediate its ends-and a plunger of substantial weight loosely fitted in said cylindrical portion and enclosing a Substantial air space between it and the closed end of the chamber, and a spring reacting on the plunger for spacing it a llimited distance away from the entrance en v 4. In the construction defined in claim l, the air-trapping chamber having its entrance end closed by a plug having a restricted port for admitting the fiuid pressure from the discharge pipe.

. 5. In combination with a pump for supplying fuel to an internal combustion engine, a verticall extending air trapping chamber closed at tllie upper end and having its lower end connected with a pump discharge pipe beyond the pump discharge valve, a loosely fitted plunger adapted to be liquid-sealed in said chamber intermediate the open and closed ends, and a relatively light spring below the plunger stopped at its lower end,

and having resilient reaction for supporting the weight of the plunger, and a plug having restricted a erture for access of fiuid pressure to ythe cliamber and closing the lower end of the chamber except as to said restricted aperture,and serving as a stop for the lower end of said spring.

In testimony whereof, I have hereunto set my hand at Chicago, Illinois, this 9th day of November, 1928.

' ENOCI-I L. PEARSQN.

llO 

